Depressants facilitate the separation of sulfide ores either by depressing gangue minerals and floating the desired mineral, or by holding down the desired mineral while floating the undesirable gangue.
It is important to note that just because a reagent is a depressant for one mineral/collector combination, it does not necessarily follow that it is a depressant for other combinations.
Depressant applications
These depressants are shown with their typical applications:
Sodium Metabisulphate – Depression of Zn sulphide (sphalerite) and Fe sulphide (eg. pyrite, pyrrhotite) minerals.
Sodium Sulphide / Sodium Hydrosulphide – At low dose rates (below 500 g/t), can be used as to depress Zn sulphide (e.g. sphalerite) and Fe sulphide (e.g. pyrite, pyrrhotite) minerals. At high dose rates (above 500g/t), it can be used to depress all sulphides (reverse flotation), allowing gangue to float and be removed.
Sodium Cyanide – Strong sulphide depressant for iron and zinc sulphides (e.g. pyrite, pyrrhotite, marcasite, arsenopyrite, sphalerite).
Lime – Depressant for pyrite during copper and zinc flotation and in other sulphide ores where pyrite is a problem.
Carboxymethyl cellulose – Depression of silicate gangue (e..g. talc, serpentine, lizardite, antigorite)
Guar Gum – Depression of silicate gangue (eg. talc, serpentine, lizardite, antigorite)
Zinc Sulphate – Depression of zinc sulphide from lead and copper sulphide minerals. Can be used alone or in conjunction with cyanide.
Dextrin – Mostly used to depress carbon minerals during sulphide flotation. Can also been used to depress galena.